Magneto-resistive head

ABSTRACT

A hard magnetic thin film magnetized in one direction is disposed on or in the vicinity of a magneto-resistive element upon which inclined electrodes are formed. A magnetic field from the hard magnetic film magnetizes the magneto-resistive element stably so that the element has a single magnetic domain. Thus, the magneto-resistive head is remarkably stable with respect to the disturbance magnetic field and inhibits Barkhausen noise from being produced. As a result, the magneto-resistive head reproduces stably and with an improved S/N ratio.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a magnetic head which ismounted on a magnetic recording, reproducing apparatus forrecording/reproducing the information stored on a magnetic recordingmedium. More particularly, the present invention relates to amagneto-resistive head.

2. Description of the Prior art

A conventional magneto-resistive head shown in FIG. 4 has been disclosedin Japanese Laid-Open Patent Publication No. 50-134624. A gap insulatinglayer 52, a rectangular magneto-resistive element 53 of a Ni-Fe alloythin film or the like, a pair of electrodes 54a, 54b, inclinedelectrodes 57a, 57b, 57c, 57d, 57e, a front yoke 56 and a back yoke 58and so on for guiding magnetic signal flux stored on the magneticrecording medium from the magnetic tape sliding face 55 to themagneto-resistive element are sequentially laminated on a magnetic baseplate 51 through an insulating layer (not shown). The magneto-resistivehead is connected to an exterior circuit through terminals 59a, 59b. Themagneto-resistive element must be of a single magnetic domain and have aspecific direction of magnetization in order to operate normally in theconventional magneto-resistive head. FIG. 5 shows an essential portionof the magneto-resistive element. When the driving current flows in thedirection of reference numeral 62, the initial magnetization of themagneto-resistive element must be in the direction shown by referencenumeral 61.

The reasons for this will be described hereinafter. If themagneto-resistive element were magnetized in mutually oppositedirections as shown by reference numerals 61, 66 in FIG. 5, the changein resistance in each portion of the element would become reverse interms of polarity when the signal magnetic field 64 flows into themagneto-resistive element. This effect extremely reduces the output.Because the reverse direction of magnetization exists within themagneto-resistive element, Barkhausen noise can be generated.

In the conventional type of magneto-resistive head, therefore, themagnetizing direction within the magneto-resistive element should be indirection 61.

However, in the conventional magneto-resistive head, the magnetizingdirection changes in a disturbance magnetic field of approximately1600A/m. The reproducing output thus becomes unstable and includesnoise.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to substantiallyeliminate the above-discussed drawbacks inherent in the prior art.

More specifically, an object of the present invention is to provide animproved magneto-resistive head which exhibits improved stability withrespect to the disturbance magnetic field, and which exhibits superiorreproducing output by inhibiting Barkhausen noise from being produced.

In accomplishing these and other objects, the present invention providesa magneto-resistive head having a hard magnetic film magnetized in aspecific direction to apply a magnetic field in the longitudinaldirection of a magneto-resistive element on which inclined electrodesare formed. The hard magnetic film magnetized in one specific directionmakes the magnetic domain of the magneto-resistive element a stablesingle magnetic domain. As a result, the magneto-resistive head of thepresent invention hardly produces Barkhausen noise. Also, thereproducing output is extremely stable with respect to the disturbancemagnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome apparent from the following description of the preferredembodiment thereof made with reference to the accompanying drawings, inwhich:

FIG. 1 is a plan view of a portion of a first preferred embodiment of amagneto-resistive head according to the present invention;

FIG. 2 is a plan view of a portion of a second preferred embodiment of amagneto-resistive head according to the present invention;

FIG. 3 is a plan view of a portion of a third preferred embodiment of amagneto-resistive head according to the present invention;

FIG. 4 is a perspective view of an outer part of a conventionalmagneto-resistive head;

FIG. 5 is an enlarged view of an essential portion of the conventionalmagneto-resistive head; and

FIG. 6 shows a reproducing waveform with Barkhausen noise.

DETAILED DESCRIPTION OF THE INVENTION

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

FIG. 1 shows a magneto-resistive element of a first preferred embodimentof the present invention. In the first embodiment, a rectangularmagneto-resistive element 11 is formed on a magnetic base plate (notshown) of a Ni-Zn ferrite or the like. Hard magnetic layers 12a, 12b,12c of a Co-P alloy thin film or a Co-Pt alloy thin film or the like areformed on the magneto-resistive element. Electrodes 13a, 13b and aninclined electrode 14c are formed on, and have a shape similar to uppersurfaces of the electrodes. The other inclines electrodes 14a, 14b, 14d,14e are formed directly on the magneto-resistive element. With the abovestructure so fabricated, the magneto-resistive head is magnetized in thelongitudinal direction 15 of the magneto-resistive element as shown. Thedriving current flows in the direction of arrow 16.

The magneto-resistive head of the first embodiment does not give rise toa large amount of Barkhausen noise. Generally, Barkhausen noise ispresent in the form shown in FIG. 6. Namely, FIG. 6 shows a reproducingwaveform 71 of the present embodiment, wherein jumps 72 appear in thereproducing waveform. The magnitude of the Barkhausen noise can beexpressed by the ratio between the amplitude H of the reproducingwaveform and the amplitude B of the jumps, i.e., B/H. The ratio B/H ofthe magneto-resistive head of the present embodiment is less than 1%. Onthe contrary, the reproducing output of the conventionalmagneto-resistive head, which does not have a hard magnetic film, islower, by about 1/2 to 1/5, than the present invention, in a disturbingmagnetic field less than 900 A/m, and has an unstable reproducing outputwhereby the Barkhausen noise is so great that the ratio B/H is more than5%.

The configuration of the hard magnetic film is determined in accordancewith the reproduction sensitivity of the magneto-resistive element andthe stability with respect to the disturbance magnetic field. Namely,the greater the number of hard magnetic film portions that are used, thestronger the magnetic field applied to the magneto-resistive element,thus increasing the stability with respect to the disturbance magneticfield. Further, the greater the number of hard magnetic film portionsthat are used, the more the magnetization of the magneto-resistiveelement lowers the sensitivity of the head because magnetization in thedesired direction becomes difficult in accordance with the signalmagnetic field. In the actual magneto-resistive head, the number of thehard magnetic layers (portions) are determined taking these points intoconsideration. In the first embodiment of the present invention, thetrack width is approximately 70 μm. The three hard magnetic layers arediscrete portions of a Co-Pt magnetic thin film, have thicknesses of0.15 μm, and are disposed at the end portions and at the center of themagneto-resistive element as spaced from one another by intervals ofapproximately 40 μm. This magneto-resistive head is stable with respectto a disturbance magnetic field of the approximately 16000A/m. Only twohard magnetic layers may be provided as disposed at the end portions ofthe magneto-resistive element with an approximately 90 μm intervaltherebetween. In other words, the layer of the Co-Pt thin film at thecentral portion of the magneto-resistive element may be omitted. In thiscase, the reproduction sensitivity is improved by approximately 2 dB andthe stability with respect to the disturbance magnetic field is loweredapproximately one half to 8000A/m. Also, the Barkhausen noise (B/H) isless than 1%. Furthermore, it is possible to space the thin layers ofCo-Pt from one another at intervals less than those mentioned above.However, if the spaces between the thin layers of Co-Pt is less than 10μm, the magnetic field generated from the thin film of Co-Pt is sostrong that the reproducing output is 1/3 that of the first embodiment,whereby the reproducing capability is insufficient.

Because the layers of the hard magnetic film are disposed at the samelocations as the electrodes in the first preferred embodiment of thepresent invention, a large reproduction sensitivity can be achievedwithout any restrictions on the effective sensitivity portion of themagneto-resistive element.

FIG. 2 shows a second embodiment of the present invention. Electrodes24a, 24b, 24c, 24d, 24e, inclined with respect to the longitudinaldirection of the magneto-resistive element 21, and electrodes 23a and23b are formed on the magneto-resistive element 21 similar to theembodiment of FIG. 1. The second embodiment of FIG. 2 is different fromthe first preferred embodiment of FIG. 1 with respect to the hardmagnetic film. Namely, a hard magnetic film 20 is located several μmaway, on the terminal side, from the magneto-resistive element 21. Thehard magnetic film is a Co-Pt thin film similar to that of the firstembodiment. The width of the film 20 is 10 μm, the film thickness is0.15 μm, and the length thereof is approximately 100 μm which are almostsame as those dimensions of the magneto-resistive element. The hardmagnetic film is magnetized in direction 25. Due to the leaking magneticfield from the film, the magneto-resistive element is magnetized in thedirection 27. The driving current flows in the direction of arrows 26 a,26b. The second embodiment of the magnetic-resistive head is stable withrespect to a disturbance magnetic field of approximately 16000A/m as inthe first preferred embodiment.

FIG. 3 shows a third embodiment of the present invention. Electrodes33a, 33b and inclined electrodes 34a, 34b, 34c, 34d, 34e are formed on amagneto-resistive element 31 as in the embodiment of FIG. 1. The thirdembodiment of FIG. 3 is different from the first preferred embodiment ofFIG. 1 and the second preferred embodiment of FIG. 2 with respect to thelocation of the hard magnetic film. Specifically, the hard magnetic film30 is formed immediately under the magneto-resistive element 31. In thiscase, an insulating layer (not shown) of SiO2 or the like and having athickness of 1 μm is formed as an intermediate layer between themagneto-resistive element 31 and the hard magnetic film 30. The hardmagnetic film is a Co-Pt thin film as in the first and secondembodiments. The shape of the film 30 is almost the same as that of themagneto-resistive element, and the thickness of the film 30 is 0.15 μm.The hard magnetic film is magnetized in the direction 35 and due to theleaking magnetic field of the film the magneto-resistive element ismagnetized in direction 37. The driving current is represented byreference numerals 36a, 36b. The third embodiment of themagneto-resistive head is stable with respect to a disturbance magneticfield of approximately 16000A/m as in the first and second embodiments.

In the magneto-resistive head of the present invention, the hardmagnetic thin film for applying the magnetic field in the longitudinaldirection of the magneto-resistive element is arranged on or in thevicinity of the MR element upon which the inclined electrodes aredisposed. Thus, the head is remarkably stable with respect to thedisturbance magnetic field. Because of this stability, i.e. the singlemagnetic domain of the magneto-resistive element, superior reproducingoutput can be obtained by the suppression of the Barkhausen noise.

Although a magnetic base plate such as Ni-Zn ferrite or the like is usedas a base plate in the first, second, and third embodiments, the sameeffect can be obtained by forming the hard magnetic thin film on anon-magnetic ceramic base plate.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to be notedthat various changes and modifications will be apparent to those skilledin the art. Therefore, unless such changes and modifications otherwisedepart from the scope of the present invention, they should be construedas included therein.

We claim:
 1. A magneto-resistive head comprising: a base plate; asubstantially rectangular magneto-resistive element extendinglongitudinally along a surface of the base plate; terminal electrodeshaving first ends connected to said magneto-resistive element and secondends remote from said magneto-resistive element; a plurality ofelectrodes disposed over said magneto-resistive element and extendinglongitudinally in a direction that is oblique to the lengthwisedirection of said substantially rectangular magneto-resistive element;and a film of a hard magnetic material applying a magnetic field in thelongitudinal direction of the magneto-resistive element, said film of ahard magnetic material being disposed along said surface of the baseplate and spaced from said magneto-resistive element toward the secondends of said terminal electrodes.
 2. A magneto-resistive head as claimedin claim 1, wherein said film of a hard magnetic material has arectangular shape similar to that of said magneto-resistive element andis disposed parallel to said element.